72 
and 110° F. Itis highly probable, then, that the high temperature of 
104° F. to 108° F. produced Aeat vigor in the pupe, and therefore the 
metabolic processes were checked, exactly as they would have been by 
the benumbing influence of cold. If this be true it becomes probable 
that the peculiar colour aberrations caused by cold are only an ex- 
pression of the decreased metabolism in the pup. It will be remem- 
bered that heat of 85° F. produces an aberration in V. antzopa which 
is just the reverse of that caused by cold. In this case the peculiar 
coloration could be explained as one of the results of the increased 
metabolism in the pupee. 
‘Now it may well be that it is an advantage to a pupa which 1s 
destined to withstand the winter’s cold to zzferit a tendency towards 
a low metabolism, for resistance to the cold would naturally require 
the possession of low metabolic processes ; hence those pupze which 
already possessed low metabolism would be in a better condition to 
withstand the effects of cold. Natural selection would then operate 
to weed out all pupz having high metabolic processes, for they 
would be more likely to freeze; whereas those individuals in which 
the metabolism was low would be preserved. Also this inherited 
tendency in the over-wintering pupze to possess low metabolic activity 
might become so strongly fixed that it would be found difficult to 
alter it by the mere subjection of the pupz to a high temperature, 
such as 78° F. to 85° F. Moreover it would doubtless be of 
advantage to the insects if they had the power to resist the influence 
of such warmth, for there are often hot periods of weather in the 
autumn, through which the over-wintering pupz must pass; but 
their development must not be hastened thereby, for if the butterflies 
emerged they or their progeny would probably perish of the cold. 
“Tn conclusion, in Lepidoptera of the temperate regions it is an 
advantage for the summer pupze to possess Azg# metabolic processes, 
for under these circumstances their development is rapid. On the 
other hand, it is an advantage to the over-wintering pup to possess 
a Zow metabolic process, for under these circumstances they would be 
the better able to withstand the influence of warm periods of weather 
in the autumn; for if the butterflies emerged at this time they or 
their progeny would probably perish of the cold. Moreover, in 
order that the pupee may withstand the influence of the winter’s cold, 
it is essential that they possess a low metabolism. Natural selection 
would then operate to cause all summer pupz to zzfer7t a high 
metabolism, while all over-wintering pupe would be forced to zzherit 
a low metabolism. Pupze which possess a constitutional tendency 
towards high metabolism give rise to the summer form of imago, 
while those pupe which possess a constitutional tendency toward low 
metabolism give rise to the over-wintered form of butterfly. The 
summer and winter forms of imago are only expressions of this 
difference in constitution of the summer and winter pupe.” 
